Methods and apparatus for forming fluff pulp sheets

ABSTRACT

An improved processes for making fluff pulp sheets mechanically eliminates many of the unwanted fiber-to-fiber bonding (fiber bundles) which may be contained in the sheet to produce consistent and uniform quality fluff pulp. Pulp slurry is deposited on a moving bottom forming wire to form a stock web. Pulp slurry is brought into contact with a moving top forming wire. The stock web is subjected to up and down dewatering creating separately formed layers to reduce fiber-to-fiber bonding. The stock web can be subjected to strong pulsating shear forces as it is being advanced along the bottom forming wire to break a majority of fiber bundles contained in the web. The pulp slurry can be deposited on the bottom forming wire utilizing a headbox with dilution control to selectively adjust the concentration of the pulp slurry. A shoe press can be used to dewater the web after it is subjected to the pulsating shear forces. The web can be dried utilizing conventional drying equipment, such as cylindrical driers.

BACKGROUND OF THE INVENTION

This invention relates generally to wet forming processes for makingfluff pulp from soften wood pulps and, more particularly, to improvedprocesses for making fluff pulp sheets which eliminate many of theunwanted fiber-to-fiber bonding (fiber bundles) that may be contained inthe sheet to produce consistent and uniform quality fluff pulp. Theseimproved processes also permit the manufacturer to control theconsistency of the stock being formed by localized dilution to achieve abetter cross-machine directional basis weight allowing the manufacturerto produce high quality fluff pulp while using low headbox consistency.Fluff pulp produced by the processes of the present invention is soft,flexible, and has a lower content of knots or hard spots. The processesof the present invention are capable of producing fluff pulp sheetshaving low variability in weight, moisture, Mullen strength and otherphysical sheet attributes. Accordingly, a fluff pulp sheet made inaccordance with the present invention should have low shred energy whilepossessing high shred quality which results in significantly reducedfiberization energy when the sheets are ultimately processed. Theinvention is especially useful for the production of fluff pulp intendedfor use as the absorbent layer in disposable diapers, sanitary napkins,absorbent hygienic products and airlaid products.

Absorbent products employing fiberized wood pulp have been available formany years. This basic wood pulp used in such products is usually termed“fluff pulp.” In the United States, fluff pulp is most typically madefrom a fully bleached southern pine kraft process pulp produced inrelatively heavy caliper, high basis weight sheets. The product isrewound into continuous rolls for shipment to the customer. Since theroll product is intended to be later reprocessed into individual fibers,low sheet strength is desirable and typically little or no refining isused prior to roll manufacturing. The requirements for surfaceuniformity and formation are similarly moderate.

At the customer's plant, the rolls are continuously fed into a device,such as a hammermill, to be reduced as much as reasonably possible toindividual fibers. Defibration is the process of freeing the fibers fromeach other before the fluff pulp enters the product forming machinery.The fiberized product is generally termed a cellulose “fluff.” Forexample, the fluff pulp can then be continuously air laid into pads forinclusion in the intended product. The most demanding application offluff pulps is in producing air-laid products, used, for example, inserving utensils and various towel applications in homes, industry andhospitals. As is mentioned above, fluff pulp sheets for air-laidproducts are usually defiberized in a hammermill. Fluff pulp sheets,however, may contain significant numbers of fiber bundles which arebonded together during the sheeting process. These unwanted fiberbundles, often referred to as knots, nits, bones and flock in theindustry, present a problem during defibration. The hammermills used forfluff production are very large energy consumers and fiber bundlespresent in the fluff pulp sheets will increase the amount of energyexpended during defibration. Also, while vigorous defiberizing canreduce the knot content, it is at the expense of considerable fiberbreakage and a high resulting content of very fine dusty material. Tooffset this problem, the pulp mill may need to add chemical debondersprior to sheet formation. Therefore, important parameters that areconsidered for dry defibration are shredding energy, i.e., the amount ofenergy needed to shred the sheet and knot content, i.e., the amount ofclumps of fibers bonded to each. In heavy manufacturing operations,reduction in energy consumption will ultimately lead to less costlyproducts. Moreover, many manufacturers require high quality fluff pulpto be used in their products due to customer demands. Accordingly,manufacturers of fluff pulp sheets are concerned in creating sheetshaving low shredding energy while still providing high quality fluff.Lower quality fluff pulp sheets cannot be used in certain applicationsand as such are often discounted for use in manufacturing lower qualityproducts.

Wood pulp softness can be expressed in terms of properties such asMullen strength (the strength of pulp or a pulp product, measured inkilopascals (kPa)), and Kamas energy (the energy required to convert agiven amount of pulp or pulp product to a fluff material, measured inwatt hours per kilogram (Wh/kg)). Mullen strength can be thought of asthe energy required to pop a hole in the sheet. Some in the industryrefer to this energy as “burst energy.” Mullen strength is a goodindicator (but not full proof) of the energy needed to shred the sheet(shred energy). Typically, the lower the Mullen strength, the easier itis to shred the fluff pulp sheet. Lower values of Mullen strength andKamas energy also correlate to softer, increasingly debonded, pulp.While it is desirable to the manufacturer to decrease Mullen strength,it should not be done at the expense of shred quality.

In the art of making fine paper, stock is usually ejected from a deviceknown in the industry as a headbox so as to land gently on the movingfabric loop, known as a forming wire, which moves at a speed typicallybetween plus or minus 3% of the wire speed, called rush and dragrespectively. In the manufacture of fluff pulp, the equipment is usuallyrun at about +10%/o rush. Excessive j/w ratio helps the Mullen strength.Water drains from the stock through the forming wire so that a web isformed on the forming wire. Excessive rush or drag can cause moreorientation of fibers of the web in the machine direction and can givediffering and sometimes unwanted physical properties in machine andcross directions. Manufacturers, therefore, are concerned about fiberorientation and accordingly have to control the orientation of fibersbeing deposited on the forming wire in order to achieve the desiredphysical properties.

As was mentioned above, wood fibers have a tendency to attract to oneanother, forming clumps, the effect being called flocculation.Flocculation is lessened by lowering consistency and or by agitating theslurry entering or in the headbox. However, defloccullation becomes verydifficult at much above 0.5% consistency. Minimizing the degree offlocculation is important to the physical properties of the fine paperor fluff pulp.

Usually, the stock is supplied at extremely high pressure to the headboxby means of pumping equipment and the stock is ejected from the headboxthrough a device known as slice lip. Accordingly, it is essential thatthe rate of flow of stock through a distributor tube disposed at oneside of the headbox be the same as the rate of flow of stock movingthrough a distributor tube disposed at the opposite side of the headbox.The rate of flow of stock is usually defined as the number of cubic feetof the stock passing a particular point every minute. It is necessarythat the rate of stock flow remain constant or as constant as possiblethroughout the headbox. The amount of fiber per unit area (basis weight)of the formed web should be ideally constant across the width of themachine and along the machine direction. If the stock has beenthoroughly mixed and if the slice lip opening is the same along theentire cross-machine directional width of the headbox, then the weightof the fibers within the stock per inch of width across the ribbon ofstock ejected through the slice lip should be substantially constant.The resulting web should then have a uniform basis weight in across-machine direction. However, in practice, it is often difficult tomaintain a constant stock supply pressure and a uniform consistent inthe stock. Accordingly, maintaining an even distribution of fiberswithin the stock present problems when endeavoring to maintain a uniformbasis weight across the width of a formed web.

The manufacturers of fluff pulp also face the problem of maintaining acontrolled cross-machine directional basis weight of the formed web.Manufacturers must control the basis weight of the formed web to improvethe quality of the end product. Accordingly, the fluff pulp manufacturermust control the basis weight without compromising fiber orientationprofile. Additionally, the manufacturer must also be mindful of the needto simultaneously minimize the degree of flocculation in order to attainthe desired physical properties of the fluff pulp.

Accordingly, it would be desirable to provide processes for formingfluff pulp sheets having improved bulk, softness and reduced inter-fiberbonding without sacrificing the absorbent properties of the pulp. Also,there has been a need for processes for producing high quality fluffpulp sheets that have significantly lower Mullen strength (burst energy)without losing shred quality. There is also a need to achieve a moreuniform basis weight profile without compromising the fiber orientationprofile. An improved and more uniform cross-directional weight basis canpromote more stable operation in the hammermill and uniform final userproduct. The novel processes of the present invention fill these andother needs.

SUMMARY OF THE INVENTION

The present invention provides novel processes for the manufacturing offluff pulp sheets having a reduced number of fiber-to-fibers bonds(fiber bundles) and low variability in weight, moisture, Mullen strengthand other physical sheet attributes. Fluff pulp sheets made inaccordance with the present invention will possess low shred energywhile retaining high shred quality. The present invention also utilizesprocesses and equipment having dilution control associated with aheadbox to achieve a very uniform cross-directional basis weight acrossthe width of the machine to thereby improve the quality of the endproduct and to run the paper forming equipment with lower headboxconsistency. The use of dilution control with the headbox improves thebasis weight profile to produce more stable operations in the hammermilland a more uniform final product.

In one particular aspect of the present invention, a pulp slurry madefrom fluff pulp fibers in an aqueous solution is deposited on the bottomwire (also known as a “forming wire”) of a paper manufacturing machineto create a stock web (also referred to as a “mat” in the industry). Dueto its nature, the pulp slurry includes both individual fibers andfibers clumped together in fiber-to-fiber bonds forming “fiber bundles.”The presence of these fiber bundles is unwanted in the formation of thefluff pulp sheet since these fiber bundles will dry and remain in thefinished sheet as unwanted clumps of fibers. Additional energy isusually needed to be expended by the product manufacturer when the fluffpulp sheets are being defiberized due to the presence of these unwantedclumps. Additionally, these fiber bundles reduce the quality of thefluff that will be produced. In one aspect of the present invention, theweb is placed on a moving bottom wire and is subjected to high pulsatingshear forces which act on the fiber bundles contained in the web tobreak a majority of them up into individual fibers or smaller sizedbundles. The web is later dewatered and dried to produce a fluff pulpsheet having reduced number of unwanted fiber bundles.

In one aspect of the present invention, the web is advanced by thebottom wire and placed in contact with a top forming wire whichcooperates with the bottom wire to press some of the liquid from theweb. The top forming wire and bottom wire can be, for example,components of a paper forming machine known as a “top former” or “twinwire” machine. In this aspect of present invention, the web is placedbetween two wires and is subjected to up and down dewatering reducingtendency of fiber to fiber bonding. The use of a top and bottom wireallows the web to be dewatered from two sides, rather than one, whichhelps to decrease the size of the fiber bundles. The use of top andbottom wires also retains the web within a somewhat confined space toallow the web to be subjected to high pulsating shear forces which actto break up fiber bundles that have formed in the web. The top formingwire former promotes better distribution of the fibers and reduceslocalized area flock that create uneven strength characteristics to thefluff pulp.

In one aspect of the present invention, a pulsating shear force can beapplied to the web in an area where the top forming wire is in contactwith the web. The pulsating forces act on the fiber bundles contained inthe formed web and are sufficiently large in magnitude to break amajority of these unwanted fiber bundles. The pulsating forces can beapplied, for example, to the web in an area where the top forming wiremakes contact with the web. The pulsating forces act on the fiberbundles contained in the formed web and are sufficiently large inmagnitude to break a majority of these unwanted fiber bundles.Thereafter, the web is fed into a pressing machine which contacts theweb to press additional liquid solution from the web. In one particularaspect of the invention, the pressing machine can be a paper formingmachine known as a “shoe press.” A shoe press can be used since thepress provides a larger “nip” area which removes liquid from the webunder a lower pressure than conventional roll presses known in the art.The shoe press provides a greater nip area which allows a reducedpressure force to be applied to the fluff pulp stock web as it movesthrough the pressing machine. Since the fluff pulp stock web has agreater thickness than conventional fine paper stock, the shoe pressallows for reduced forces which helps to prevent compression of the pulpfibers while still providing substantial dewatering capabilities. Asingle shoe press or multi shoe presses in series could be implementedfor dewatering purposes. The shoe press could be combined with otherpressing machines, such a roll presses, to progressive dewater the web.Lastly, after the web has been dewatered by the respective pressingmachines, heat can be applied to the web (via driers) to evaporateadditional liquid from the web.

In another aspect of the present invention, a vacuum can be applied tothe web when the pulsating shear forces are being applied to the web.The vacuum can be applied at the same location where the pulsating shearforces are being applied to the web to increase the shearing actionimparted on fiber bundles contained in the web. This increased shearingforce created by the vacuum helps in the breaking of the fiber-to-fiberbonds found in the formed web.

In another aspect of the present invention, the pulp slurry can bedeposited on the bottom wire using a headbox which has dilution control.In this particular aspect of the invention, a liquid, such as water,could be selectively added to the pulp slurry to adjust the consistencyof the slurry being deposited on the bottom wire in allow themanufacturer to adjust the cross-directional basis weight of the webbeing formed. In this regard, a more uniform cross-machine directionalweight basis can be attained without compromising fiber orientation.

In other aspects of the invention, more than one type of pulp slurrycould be utilized to create a fluff pulp sheet having multiple layering.Additives, such as a colorant, could be added to the slurry(es) in otheraspects of the invention. A multiple layering headbox with or withoutdilution control could be used to deposit the stock slurry on the bottomwire. Alternatively, multiple headboxes with or without dilution controlcould be used to create the multilayered fluff pulp sheet withadditives. After the web has been subjected to the pulsating shearforces, it can be further dewatered in pressing equipment such as a shoepress or a series of shoe presses. In another aspect of the invention,additional pressing equipment such as roll presses could be used withthe shoe press to further dewater the web.

Other features and advantages of the present invention will become moreapparent from the following detailed description of the invention, whentaken in conjunction with the accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a process of forming a continuous fluffpulp sheet in accordance with the present invention.

FIG. 2 is a schematic drawing showing an enlarged image of the topformer or twin wire machine depicted in FIG. 1 which can be used toapply the pulsating shear forces on the stock web as it is beingadvanced to the downstream dewatering machines.

FIG. 3 is a schematic drawing which depicts the top and bottom blades ofthe top former of FIG. 2 in greater detail.

FIG. 4 is a flow diagram which depicts the processes and machinery whichcan be used in forming fluff pulp sheets in accordance with the presentinvention.

FIG. 5 is a flow diagram which depicts alternative processes andmachinery which can be used in forming fluff pulp sheets in accordancewith the present invention.

FIG. 6 is a flow diagram which depicts alternative processes andmachinery which can be used in forming fluff pulp sheets in accordancewith the present invention.

FIG. 7 is a schematic drawing showing multi layered fluff pulp sheetswhich can be formed using the processes of the present invention.

FIG. 8 is a schematic drawing showing alternative multi-layered fluffpulp sheets with additives which can be formed using the processes ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 show with schematic figures one particular process inaccordance with the present invention for forming fluff pulp sheets. Inaccordance with the process depicted in FIG. 1, a pulp slurry 10 isdelivered from stock container 12 to a headbox 14. The stock container12 holds the processed pulp slurry after it has been prepared utilizingknown techniques in the art. As noted above, the pulp slurry 12, alsoreferred to as “pulp stock,” may typically include cellulose fibers suchas chemically digested wood pulp fibers as its main component which issuspended in water or a water-based liquid solution. The slurry may alsoinclude as a minor component, mechanical wood pulp and synthetic orother non-cellulose fibers, chemical surfactants and other elementsknown in the paper making art. Preferably, but optionally, the pulpslurry has undergone a bleaching process to create white fluff pulpstock. The pulp slurry exits the headbox 14 through an opening ofadjustable height called the slice 16 and is carefully deposited so asto land gently onto a moving fabric loop, herein referred to as thebottom forming wire 18 which may be found on conventional Fourdriniermachines or “top former” or “twin wire” machines which include a secondwire which contacts the web (discussed in greater detail below).

The term “wire” is well known in the art and generally refers to aspecially woven plastic or fabric mesh conveyor belt which is used tocreate a continuous paper web that transforms the source of wood pulpinto a sheet of paper. It should be appreciated that many differenttypes of wires could be used in accordance with the processes of thepresent invention.

It should be appreciated that the bottom forming wire 18 is shownschematically since any one of a number of paper forming equipment couldbe implemented in accordance with the present invention. The pulp slurryis deposited at a speed typically about plus 10% rush. The higher rushpercentage helps to produce a suitable Mullen strength in the fluffpulp. Water drains from the stock through the forming wire so that a web20 is formed on the bottom forming wire. Excessive rush or drag willcause more orientation of fibers of the web 20 in the machine directionand typically creates very poor contact between fibers which wouldproduce in fine paper manufacturing differing and sometimes unwantedphysical properties in the machine and cross directions of the finepaper, but with fluff pulp will reduce shredding energy and fiber tofiber bonds. Manufacturers, therefore, are concerned about fiberorientation and accordingly have to control the orientation of fibersbeing deposited on the forming wire in order to achieve the desiredphysical properties.

To achieve a better cross direction weight basis, the process of thepresent invention utilizes a headbox 14 may include dilution controls(not shown) which allow the operator to dilute the consistency of thepulp slurry as it exists the headbox 14 and is deposited onto the bottomwire 18. Accordingly, the headbox 14 would include dilution lines (notshown) or other liquid supply equipment for controlling the dilution ofthe pulp slurry flowing through the headbox in order to control thecross-machine direction basis weight of the web 20 that is beingproduced. The use of dilution control associated with the headbox 14achieves a very uniform cross-directional basis weight across the widthof the machine to thereby improve the quality of the end product andallows the manufacturer to run the equipment with lower headboxconsistency. This part of the process allows the slurry of pulp fibersto be filtered out onto the continuous bottom forming wire 18 to form awet web of fiber having a specific basis weight. In this manner, thepresent invention is capable of controlling the basis weight of theformed web to improve the quality of the end product. This aspect of thepresent invention thus controls the basis weight without compromisingfiber orientation profile.

The stock web 20 which is initially deposited on the bottom wire 18 isquite soft and wet due to the presence of a high amount of the liquidmaking up the pulp slurry. Accordingly, as is known in paper-making art,the liquid must be drained from the web 20 (referred to as “dewatering”)in order to ultimately produce a dry fluff pulp sheet. In this regard,drainage units 22 can be located under the table where the web 20 isinitially deposited on the bottom wire 18 to allow liquid to drainthrough the small openings formed in the bottom wire 18. However, thesedrainage units 22, which may include vacuum or suction devices to drawout the liquid, are not capable of completely drying the web 20.Additional drying equipment must be used to progressively dewater thestock web 20. The web 20 moves along with the bottom wire in thedirection depicted by arrow 24. The web 20 is the fed into a top former26 which includes a second top forming wire 28 that contacts the top ofthe web 20 and, in conjunction with the bottom wire 18, helps to pressadditional liquid from the wet web 20. The web 20 entering the topformer 26 typically has a dryness of about 2-4%.

As can be best seen in FIG. 2, the top wire 28 converges with the bottomwire 18 along a length of the top former 26 to allow sufficient pressingforces to be attained to press some of the liquid from the web 20.Additionally, the top former 26 has dewatering chambers 30 which includevacuum sources (not shown) that draw liquid from the web 20 passing overthe vacuum into individual storage containers 32A-32C. The vacuum(depicted by arrows in FIGS. 2 and 3) for the first container 32A can berun at a lower rate than the later containers 32B and 32C. For example,the vacuum associated with container 32A could run at about 5-10 kPa.The vacuum associated with the second container 32B could run at about5-20 kPa. Lastly, the vacuum associated with the third container 32Ccould be run at about 10-25 kPa. It should be appreciated that thenumber of containers and the vacuums associated with each container canvary depending upon the weight basis of the fluff pulp sheet beingcreated. Additionally, one or more suction boxes 34 could be placedbelow the bottom wire 18 to draw liquid from the web 20 as well.Typically, the web 20 would leave the top former 26 at about 8-14%solids.

The top wire 28 of the top former 26 and bottom wire 18 convergetogether by utilizing a set of top blades 36 located beneath thedewatering chambers 30 along with preferably a set of bottom loadableblades 38 located directly beneath the bottom wire 18. These blades 36and 38 can be made from materials such as ceramics. These loadableblades 38 (the loading element) are designed to move the bottom wire 18upward so that the top wire 28 comes in contact with the top blades 36.This and vacuum between blades 36 results in a pinching effect whichcauses some of the liquid to be squeezed from the web 20 and forming afiber layer against top wire 40 which is separate from formed layer inthe bottom 42. These separately formed layers have a low tendency offiber to fiber bonding. As can best be seen in FIG. 3, the top blades 36are generally stationary while the bottom blades 38 are movable. Theplacement of the bottom blade 38 between adjacent top blades 36 causesthe top and bottom wires to move in an acute upward and downward motionwhich creates the strong pulsating shear forces that are, in turn,transferred to the web 20 as it passes through the top former 26. Thesestrong pulsating shear forces are designed in order to break the manyfiber bundles present in the wet web. Since the web 20 has a high stateof wetness when entering the top former 26, any fiber bundles containedin the web are still very susceptible to shear forces which can breakthe fiber-to-fiber bonds. A suitable device which utilizes top andbottom blades for loading the top and bottom wires of a top former isdisclosed in U.S. Pat. No. 5,695,613, which is incorporated in itsentirety herein.

It should be appreciated that in the art of forming fine paper stock, avery low load is normally applied by the bottom blades 38 during thesqueezing or dewatering process since medium or high pulsating shearforces could be detrimental to the thin stock web being formed on thetop former. However, as is discussed in greater detail below, highpulsating shear forces are desired in the processes of the presentinvention since the pulp slurry forming the web 20 contains manyfiber-to-fiber bonds. The pulp slurry contains numerous pulp fiberswhich cannot possibly be free of fiber-to-fiber bonds as the slurryexits the headbox 14. The dilution of the pulp slurry may lead to someof the fiber bundles being broken as the slurry exits the headbox.However, there may still be many fiber-to-fiber bundles which will bedispersed within the stock web. Also it is known in art of paper makingthat fibers have a tendency to create fiber-to-fiber bundles in stock.For these reasons, the number of fiber bundles remaining in the stockweb 20 is of great concern to the fluff pulp manufacturer. Accordingly,some manufacturers suggest mechanical steps or chemical treatment to beemployed during the time that the pulp slurry is first being processedto reduce the number of fiber bundles that enter the headbox. Forexample, in U.S. Pat. No. 6,059,924, a process is disclosed in which thepulp slurry is mildly refined prior to the step of sheet formation. Sucha process requires additional equipment to be used to refine the pulpslurry before it enter the headbox. Other methods to deal with theproblem of unwanted fiber bundles require chemical additives to be addedto the pulp slurry. However, these processes can lead to additionalcosts in manufacturing the fluff pulp sheet.

The processes of the present invention utilize high pulsating shearforces which break up the fiber bundles once the web 20 has beendeposited on the bottom wire 18. In this regard, the blades 36 and 38 ofthe top former provide one type of suitable mechanism which is capableof producing cyclical, pulsating shear forces which act on the web 20 asit passes over the blades. The pulsating shear force is usuallynon-uniform which causes the web 20 to undergo extreme fluctuations ofshear forces to help to break any type of fiber-to-fiber bonds that aredispersed in the web. The timing of the application of these highpulsating shear forces occurs when the web 20 is still very wet (onlyabout 2-4% dry) since bonds in wet slurry are easier to break withapplied pulsating forces.

As can be seen in FIG. 3, the bottom blade 38 is pushed upward to nearlybetween two top blades 36 to place a considerable force on the web 20 asit passes over this region of the top former. This creates an acute,upward and downward motion which produces the pulsating shear force thatis applied to the web 20. As can be further seen in FIG. 3, the web 20has a thinly dried upper surface 40 and lower surface 42 with a middleportion 44 that remains substantially in a fluid state as the web 20passes along the blades 36 and 38. The combination of the vacuum(depicted by arrows inn FIG. 3) in the dewatering chambers 30 combineswith the pulsating shear forces produced by the top and bottom blades 36and 38 to create shear forces that are strong enough to break most, ifnot all, of the fiber bundles present within the thin upper and lowersurfaces 40 and 42 along with the fluid middle portion 44. However, theintegrity of the fluff pulp sheet will not be effected by the poundingit receives during this portion of the process since the placement ofthe top wire 28 and bottom wire 18 helps to maintain the web 20 intactas it moves through and eventually exits the top former 26. As the web20 proceeds to the next dewatering equipment, a significant amount ofsolution has been removed from the web 20, but more importantly, asignificant amount of the fiber-to-fiber bundles have been broken, whichwill result in a more uniform fluff pulp sheet. After top former web 20dryness is high enough that it avoids fibers to move freely relative toeach other avoiding new flock formation.

The dewatering in the dewatering chambers 30 will form a fiber layer 40against top wire which is separate to layer formed on bottom wire 42with drainage units 22. As these layers are formed separately the fibersare not tangled together due the fluid middle portion 44, thefiber-to-fiber bonding is reduced compared to traditional sheet whichhas only one direction dewatering during forming. Two layered formingadditionally will reduce size and number of the fiber bundles like doesthe shear effect with loading elements. These effects will reduce energyrequired to break the web in to individual fibers in Hammer mill orsimilar equipment.

After the web 20 exits the top former 26, it still has considerablewetness and needs to be dewatered by additional dewatering machines. Ascan be seen in FIG. 1, the web 20 initially enters a roll press 50,illustrated in this case as two sets of felted calendar rolls 52, 54,each defining a respective nip through which the web 20 passes. Afterexiting the first roll press 50, the web 20 enters a shoe press 56 whichis schematically shown as including a pair of rollers 60 and a movableshoe 58 that places a loading force on the web 20. The shoe pressincludes rollers 62-68 which are used to advance a felt belt 70. Theshoe press is particularly useful in the dewatering process since theshoe 58 can be designed to have a larger contact area (nip) thanconventional roll presses. Accordingly, the larger nip of the shoe pressallows more contact surface, longer dwell time in the nip, with the web20 resulting in greater drainage of liquid from the web. Additionally,due the larger surface area of the shoe press, a smaller peak pressureduring the nip is required to be applied by the shoe. Since thethickness of the web can be quite large, pulp manufacturers would prefernot to squeeze the web too much since the fiber mat can becomecompressed during the dewatering process. The shoe press 56 thus helpsto prevent unwanted compression of the web. The web 20 then exits theshoe press 56 and can enter into another pressing machine such asanother roll press 72, again illustrated as two sets of calendar rolls74, 76, each defining a respective nip through which the web 20 passes.

From the dewatering section, the web enters a drying section 80 of thefluff pulp manufacturing line. In a conventional fluff pulp sheetmanufacturing line, drying section 80 may include multiple cylinder ordrum dryers with the web 20 following a serpentine path around therespective dryers and emerging as a dried sheet or mat 82 from theoutlet of the drying section. Alternate sides of the wet web 20 will beexposed to the hot surfaces as the web 20 passes from cylinder tocylinder. In most cases, the fluff pulp web 20 is held closely againstthe surface of the dryers by a fabric having carefully controlledpermeability to steam and air. Heat is transferred from the hot cylinderto the still wet web, allowing some of the remaining liquid to beevaporated. Other alternate drying equipment, alone or in addition tocylinder or drum dryers, may be included in the drying process.Typically, the dried pulp sheet 82 emerging from the drier section hasan average maximum moisture content of no more than about 5% by weightof the fibers, more preferably no more than about 6% to 10% by weightand most often about 7%.

In the FIG. 1 embodiment, the dried sheet 82 is taken up on a roll 84for transportation to a the fluff pulp processing equipment where thesheet can be defiberized for use in manufacturing fluffed pulp absorbentproducts. Alternatively, the dried sheet 82 can be collected in a balingapparatus 86 from which bales 88 of individual fluff pulp sheets arecreated and bundled together.

Referring now to FIG. 4, a flow chart shows the sequence of steps thatcan be performed in forming a fluff pulp sheet in accordance with theprocesses of the present invention. Initially, a pulp slurry can beprepared utilizing traditional single ply stock techniques which arewell known in the art. The stock preparation could optionally includethe bleaching of the wood pulps using known bleaching methods, includingfor example and without limitation those described in U.S. Pat. No.6,893,473. Next, the pulp slurry is delivered into a headbox which mayor may not include dilution controls to dilute the concentration of theslurry as it is being delivered onto the bottom wire. The bottom wireand top wire can be a part of a top former machine well known in theart. The top former can be set to apply a high pulsating shear force onthe stock web. The web formed on the bottom wire can then be advancedinto a number of different machines and combinations of machines toassist in dewatering the web. For example, a single shoe press could beused to dewater the web. Another alternative is to use multiple shoepresses in series to progressively dewater the web. Another alternativeis to use one or more roll presses with a single shoe press. Thedewatering process could use single or multiple roll presses and shoepresses to progressively dewater the web. Any of the presses can besingle or double felted. Accordingly, there are numerous ways associatedwith the processes of the present invention to effectively dewater theformed web. Lastly, the web would exit the dewatering machinery toadvance the web into a dryer section. As is mentioned above, the dryersection can be created utilizing a number of different drying equipmentwell known in the art, such as cylindrical driers, which help to promotebetter separation of the fibers and to reduce bonding of the fibersresulting in a lower Mullen strength.

Referring now to FIG. 5, another flow chart shows the sequence of stepsthat can be performed in forming fluff pulp sheets in accordance withthe processes of the present invention. Initially, multiple pulpslurries are prepared utilizing multilayering stock preparation. Suchtechniques are well known in the art. The stock preparation couldoptionally include the bleaching of the wood pulps using known bleachingmethods, including for example and without limitation those described inU.S. Pat. No. 6,893,473. Next, the pulp slurries are delivered into aheadbox which may or may not include dilution controls. if dilutioncontrols are available, the concentration of the slurries can be dilutedas the slurries are being deposited on the bottom wire. Alternatively,the pulp slurries could be delivered to multiple headboxes with orwithout dilution. An individual headbox could be used to deposit aparticular slurry to the bottom wire. A top former machine could be usedas is described in greater detail above to break many of the fiberbundles dispersed thoughout the stock web. The multiple slurriescontained in multiple headboxes could be deposited on multiple topformers and Fourdriniers. The resulting webs formed by either of theseprocesses could then be dewatered utilizing, for example, a single shoepress or multiple shoe presses in series. Multiple roll presses could beused as well. Any of the presses can be single or double felted. The webwould then exit the dewatering machinery and be advanced into a dryersection as is disclosed above.

FIG. 7 shows a schematic which depicts a multilayered fluff pulp sheet90 which include a top section 92, a middle section 94 and a bottomsection 96. The top and bottom sections 92 and 96 can be made, forexample, from the same fluff material while the center section could bemade from a different fluff material. All of the layers could be madefrom different stock as well. The fluff pulp sheet can be made with anynumber of layers. Accordingly, it should be appreciated that there canbe a number of different combination of layers and the composition ofthe layers that can be created using the processes disclosed herein.

Referring now to FIG. 6, another flow chart shows the sequence of stepsthat can be performed in forming fluff pulp sheets made with additives.Initially, multiple pulp slurries are prepared with additives, such ascoloring, debonding, odor-control, static control and the like, usingadditive multilayering stock preparation techniques well known in theart. Next, the pulp slurries are delivered into a multilayering headboxwhich may or may not include dilution controls to dilute theconcentration of the slurries as they are being delivered onto thebottom wire. The slurries can then be deposited on a bottom wire of atop former machine. The resulting webs could then be dewatered utilizingthe dewatering equipment disclosed in the previous charts. For example,a single shoe press or multiple shoe presses in series could be used todewater the web. Alternatively, multiple roll presses and a single shoepress or multiple shoe presses could be used to dewater the web. Lastly,the web would exit the dewatering machinery and be advanced into a dryersection. Of course, such additives mentioned above could optionally beapplied to the web in addition to, or alternatively, at any stage,embodiment, or objective of the fluff pulp sheet making processdescribed herein below or herein above, including without limitationsurface applications including without limitation spray, coating, or thelike surface applications.

FIG. 8 shows a schematic which depicts an additive multilayered fluffpulp sheet 100 which include a top section 102, a middle section 104 anda bottom section 106. The top and bottom sections 102 and 106 can bemade from the same fluff material and the same additives while thecenter section 104 could be made from the same or a different fluffmaterial. The additives of this center section 104 could be differentfrom those used in the top and bottom sections. The fluff pulp sheet canbe made with any number of layers, each layer having different orsimilar additives. Accordingly, it should be appreciated that there canbe a number of different combination of layers and additives added to aparticular layer using the processes disclosed herein.

The various equipment which can implemented to achieve the variousprocesses described herein are generally commercially available. Forexample, a simple headbox which can be utilized can be Model Valleymanufactured by Voith Paper. A suitable headbox with dilution controlsincludes Model SymFlo manufactured by Metso Paper and Model Valleymanufactured by Voith Paper. A suitable multilayering headbox includesModel SymFlo manufactured by Metso Paper. The top former used to applythe pulsating force and vacuum to the formed web include Model MBmanufactured by Metso and Model PFI manufactured by Johnson Foils.Suitable shoe presses include Model OptiPress manufactured by MetsoPaper and Model NipcoFlex manufactured by Voith Paper. Roll presses thatcan be used include Model Combi Press manufactured by Beloit. The dryingequipment includes suitable equipment such as Model SymDry manufacturedby Metso Paper and Model Airborn manufactured by Andriz.

Generally, any fluff pulp or fluff pulp fiber is suitable for use in thepresent application, and the selection thereof is within the skill ofone knowledgeable in the fluff pulp and fluff pulp fiber arts. The typeof fluff pulp or fluff pulp fiber suitable for use herein is notintended to be limiting. Fluff pulp typically includes cellulosic fiber.The type of cellulosic fiber is not critical, and any such fiber knownor suitable for use in fluff pulp paper can be used. For example, thefluff pulp can made from pulp fibers derived from hardwood trees,softwood trees, or a combination of hardwood and softwood trees. Thefluff pulp fibers may be prepared by one or more known or suitabledigestion, refining, and/or bleaching operations such as, for example,known mechanical, thermomechanical, chemical and/or semichemical pulpingand/or other well-known pulping processes. The term, “hardwood pulps” asmay be used herein include fibrous pulp derived from the woody substanceof deciduous trees (angiosperms) such as birch, oak, beech, maple, andeucalyptus. The term, “softwood pulps” as may be used herein includefibrous pulps derived from the woody substance of coniferous trees(gymnosperms) such as varieties of fir, spruce, and pine, as for exampleloblolly pine, slash pine, Colorado spruce, balsam fir and Douglas fir.In some embodiments, at least a portion of the pulp fibers may beprovided from non-woody herbaceous plants including, but not limited to,kenaf, hemp, jute, flax, sisal, or abaca, although legal restrictionsand other considerations may make the utilization of hemp and otherfiber sources impractical or impossible. Either bleached or unbleachedfluff pulp fiber may be utilized. Recycled fluff pulp fibers are alsosuitable for use. When bleached, any bleaching method is suitable,including for example and without limitation those described in U.S.Pat. No. 6,893,473. The fluff pulp and fluff pulp fibers may be treatedor untreated, and they may optionally contain one or more than oneadditives, or combination thereof, which are known in the art. Given theteachings herein, the level of treatment, if desired, and the amount ofadditives may be readily determined by one of ordinary skill in thefluff pulp and fluff pulp fiber arts.

In the broad aspects of the present invention, it is also contemplatedthat the pulp may be treated with bond-inhibiting chemical substances,debonders as they are commonly called, chemical softeners, or otherchemical additives during preparation of the fluff pulp sheet to alterprocessing or aesthetic characteristics of the finished fluff pulp orfinished fluffed pulp and the absorbent products made from said fluffedpulp. The addition of such chemicals is normally effected by adding thechemical to the pulp prior to sheet formation in multi or single layersor by spraying the pulp after the formation of the non-woven web andsometimes during initial mechanical dewatering. Included within suchmaterials are fatty acid soaps, alkyl or aryl sulfonates, quaternaryammonium compounds and the like. Usually, such materials would be usedin an amount of below about 0.5% by weight and often below about 0.1% byweight of dry pulp.

As discussed herein, if desired, additives such as pH adjusting agent,whitener, colorant, odor-control, pigment, optical brightening agent,wetting agent, binder, bleaching agent, trivalent cationic metal, alum,other additive, or a combination thereof may be utilized. Such compoundsare known in the art and otherwise commercially available. Given theteachings herein, one of ordinary skill in the fluff pulp and fluff pulppapermaking arts would be able to select and use them as appropriate. Ifpresent, the amount of additive is not particularly limited. Of course,such additives mentioned above could optionally be applied to the web tany stage, embodiment, or objective of the fluff pulp sheet makingprocess described herein below or herein above, including withoutlimitation surface applications including without limitation spray,coating, or the like surface applications.

The dried sheet of fluff pulp fibers typically has a thickness of about20 to 80 mils, a basis weight of 200 to 900 g/m.sup.2, a burst index of0.5 to 3.0 kPa.multidot.m.sup.2/g. The dried pulp sheet generally has adensity of about 0.3 to about 1.0 g/cm.

In one embodiment, the additive may be present in amounts ranging fromabout 0.005 to about 50 weight percent based on the weight of the fluffpulp sheet. This range includes all values and subranges therebetween,including about 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.02, 0.03,0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7,0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, and50 weight percent, or any combination thereof, based on the weight ofthe finished fluff pulp sheet.

In one embodiment, the fluff pulp sheet may have a basis weight rangingfrom 100 to 1100 gsm. This range includes all values and subrangestherein, for example 100, 125, 150, 175, 200, 225, 250, 275, 300, 400,500, 600, 700, 800, 900, 1000, 1100, or any combination thereof or rangetherein.

The fluff pulp sheet made in accordance with the present invention canbe made into a number of different products. These products include, butare not limited to, absorbent products, paper products, personal careproducts, medical products, insulating products, construction products,structural material, cement, food products, veterinary products,packaging products, diaper, tampon, sanitary napkin, incontinent pads,absorbent towels, gauze, bandage, fire retardant, and combinationsthereof.

Numerous modifications and variations on the present invention arepossible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the accompanying claims, theinvention may be practiced otherwise than as specifically describedherein.

I claim:
 1. A process for making a fluff pulp sheet, comprising:creating a pulp slurry which includes pulp fibers suspended in a liquid,the pulp slurry containing multiple fiber bundles formed from pulpfibers which are bonded together and dispersed within the pulp slurry;applying an amount of the pulp slurry onto a moving bottom forming wireto form a web thereon, the pulp slurry being dispensed by a headbox; andcontrolling the cross-directional weight basis of the web by varying theconcentration of the pulp slurry being deposited from the headbox ontothe bottom forming wire.
 2. The process in claim 1, further including:applying a top forming wire onto the web and dewatering the web throughthe top forming wire to create a top fiber layer against the top formingwire.
 3. The process in claim 2, further including: dewatering the webthrough the bottom forming wire to create a bottom fiber layer againstthe bottom forming wire.
 4. The process in claim 3, further including:applying pulsating shear forces on the web as it moves on the bottomforming wire, the pulsating shear forces being sufficiently large tobreak some of the fiber bundles.
 5. The process in claim 4, furtherincluding: further dewatering liquid from the web after the web has beensubjected to the pulsating shear forces.
 6. The process of claim 1,further including: applying heat to the web.
 7. The process of claim 1,wherein liquid is added to the pulp slurry exiting the headbox to adjustthe concentration of the pulp slurry prior to being deposited onto thebottom forming wire.
 8. The process of claim 2, wherein the top formingwire contacts the web and the pulsating shear force is applied in aregion where the top forming wire and bottom forming wire contact theweb.
 9. The process of claim 2, wherein the pulsating shear force iscreated by advancing the bottom forming wire over a series of uprightmembers which cause the bottom forming wire to move in an up and downmotion.
 10. The process of claim 9, wherein a portion of the pulsatingshear force applied to the web is created by subjecting the web to avacuum source in the region where the bottom forming wire is advancedover the series of upright members.
 11. The process of claim 2, whereinthe top forming wire and bottom forming wire are components of a topformer apparatus.
 12. A process for making a fluff pulp sheet,comprising: creating a pulp slurry which includes pulp fibers suspendedin a liquid, the pulp slurry containing multiple fiber bundles formedfrom pulp fibers which are bonded together and dispersed within the pulpslurry; applying the pulp slurry onto a moving bottom forming wire whichmoves the deposited pulp slurry in a forward direction to form a web,the pulp slurry being dispensed by a headbox; and adjusting thecross-directional weight basis of the pulp slurry by diluting at least aportion the concentration of the pulp slurry as it is being depositedfrom the headbox onto the bottom forming wire.
 13. The process of claim12, further including: monitoring the cross-directional basis weight ofthe web.
 14. The process of claim 12, further including: applying apulsating shear force of sufficient magnitude on the web to break someof the fiber bundles contained in the web.
 15. The process in claim 12,further including: applying a top forming wire onto the web anddewatering the web through the top forming wire.
 16. The process ofclaim 12, further including: contacting the web with a dewateringmachine which further dewaters the web.
 17. The process of claim 16,wherein the dewatering machine is a shoe press.
 18. A process for makinga fluff pulp sheet, comprising: creating a pulp slurry which includespulp fibers suspended in a liquid, the pulp slurry containing multiplefiber bundles formed from pulp fibers which are bonded together anddispersed within the pulp slurry; placing the pulp slurry into a headboxhaving dilution control which allows the concentration of the pulpslurry to be diluted as the pulp slurry exits the headbox; applying thepulp slurry onto a moving bottom forming wire which moves the depositedpulp slurry in a forward direction to form a web; contacting the webwith a top forming wire which cooperates with the bottom forming wire todewater liquid from the web; contacting the web with a dewateringmachine which contacts the web to remove some of the liquid from theweb; and applying heat to the web to evaporate additional liquid fromthe web.
 19. The process of claim 18, further including: selectivelyadding liquid to the pulp slurry as it exits the headbox onto the bottomforming wire.
 20. The process of claim 18, further including: applying asecond pulp slurry to the first mentioned pulp slurry to form amultilayer web.